The purpose of this research is to measure the effects on oxygen delivery of several physical and biochemical properties of the erythrocyte which are frequently affected by both pathological processes and pharmacologic agents. These properties include red cell size, shape, deformability, membrane structure, metabolism and surface charge. Using a device previously developed in our laboratory, oxygen exchange rates will be measured in vitro in suspensions of red cells specifically altered with respect to the variables mentioned. In vivo analyses will include observations of the effects of altered red cells on microcirculatory flow patterns and oxygen availability in polarographic electrode-containing rabbit ear chambers. Finally, the influences of selected erythrocyte modifications on general hemodynamic and respiratory functions and on tissue oxygen delivery will be studied in a series of isovolemic exchange transfusion experiments in rabbits with multiple chronically-implanted tissue oxygen electrodes. It is hoped that information gained during this research may have application in the development of a therapeutic method for the alleviation of tissue hypoxia.